Dietary nano‑chromium picolinate enhances interferon-gamma expression in heat-stressed broilers vaccinated against Newcastle disease.

Poultry immunity is negatively impacted by heat stress (HS), resulting in reduced efficacy of vaccines. In this study, we determined whether dietary chromium (III) picolinate (CrPic) and the nano formulation (Nano-CrPic) could help alleviate the negative effects of HS on cellular immunity in vaccinated broilers against Newcastle disease (ND). Ross 308 broilers were subjected to continuing heat exposure and received supplementations of either CrPic or Nano-CrPic at 500, 1000, or 1500 ppb. Following ND vaccination, we quantified the expression of IFN-γ mRNA from splenic tissues. Importantly, IFN-γ expression increased between about 2.5-4 fold in vaccinated versus control broilers at 3 days after vaccination. In addition, under HS conditions, Nano-CrPic at 500 and 1000 ppb increased IFN-γ expression by 35-50 % compared to broilers in the HS Controls (p < 0.01) and 20-30 % compared to broilers fed traditional CrPic at comparable levels of supplementation. On the other hand, no significant change in IFN-γ expression was observed following either CrPic or Nano-CrPic supplementation in non-vaccinated birds. Supplementation with Nano-CrPic at the highest-level of 1500 ppb had diminished enhancements on IFN-γ expression, suggesting a non-linear dose-response pattern. The findings indicate that dietary supplementation using Nano-CrPic at 500-1000 ppb provides a practical means of improving cellular immunity responses that are generated after vaccination, particularly in heat-stressed broilers, thereby improving potential vaccination response under heat stress.